Automatic variable pitch propeller



Sept. 22, 1936. z. RIDDLE AUTOMATIC VARIABLE PITCH PROPELLER Filed June 25, 1930 2 Sheets-Sheet l INVENTOR.

245" fi/aozf ATTORNEY Sept. 22, 1936. I Z, RlDDLE 2,054,947

AUTOMATIC VARIABLE PITCH PROPELLER Filed June 25, 1930 2 Sheets-Sheet 2 IN VEN TOR; ZZZ/E 80045 7 ATTORNEY Patented Sept. 22, 1936 UNITED STATES PATENT OFFICE My invention relates to automatic variable pitch propellers, and the objects of my invention are:

First, to provide a propeller of this class in I which the pitch automatically changes according to the density of the air so as to absorb the power of the airplane engine at its rated speed at any altitude; v I I Second, to provide a propeller of this class in which the thrust or traction of the propeller may remain constant for all altitudes or ac-' tually increase with altitude if desired; Third, to provide a propeller of this class which eliminates the haphazard arrangement of manually adjusting the usual variable pitch pro.-

peller and the complicated controls therefor; Fourth, to provide a propeller of this class in a which the pitch maybe varied by changing the speed of the engine as well as by change of air density, so that the pilot may exercise a certain control of the propellerpitchby varying the engine speed and thereby compensate forconditions other than variation in air density, as when the weight of the airplane is changed in night;

Fifth, to provide a propeller of this class in which at idling speeds the pitch may be so low a which is particularly adapted for use in connection with airplane engineshaving super-chargers, suchengines .being capable of delivering sealevel power at high altitude Seventh, to provide a propeller of this class which increases the altitude and speedpe rformance of an airplane;

Eighth, to provide a variable pitch propeller in-which the drag and parasite resistance is not appreciably increased. and which is fully 46 capable of rotating at the speeds of conventional non-variable propellers; v

Ninth, to provide a propeller of this class which responds quickly to sudden changes in air density. whereby the airplane may maintain 50 a more level flight under "bumpy conditions; Tenth, to provide a propeller of this class which prevents overspeeding or racing- .of the engine;

Eleventh, to'provide a propeller of this class 68 which is light, though of construction,

and requires but little movement of its parts to shift the propeller blades, whereby wear is re-' duced to a minimum; and

Twelfth, to provide a propeller of this class which is sturdy of construction, durable, em- 5 cient in its action, which isnot affected by exy treme temperatures or weather conditions, and which will not readily deteriorate or get out of order. I

, with these and other objects in view as will 10- appear hereinafter, my invention consists of certain novel features of construction, combination and arrangement of parts and portions as will be hereinafter described in detail and particularly set forthin the appended claim, 15 reference being had to the accompanying drawings and to the characters of reference thereon, which form a part of this application, in which:

Figure 1 is a transverse sectional view substantially through l-l of Fig. 6, with parts 20 and portions shown in elevation; Fig. 2 is a ,Figs. 4 and 5 are sectional views of the propeller taken through H and 5-5, respectively, of. Fig. 1; Fig. 6 is a sectional view through 6-6 of Fig. 1, with parts and portions as shown in "elevation; Fig. 7 is a sectional view substantially 30 through 1-! of Fig. 1, with parts and portions nor shafts 8, governor gears 9, governor arms 40' I0, springs ll, spring anchors i2, and modified propeller blade l3 constitute the principal parts and portions of my novel automatic variable pitch propeller.

A hub casing I is provided, which is substantially in the-form of a short annular cylinder.

' At its forward portion, the hub casing is .pro-

vided with inwardlyand forwardly extending webs la, which join a hub lb located concen tricallyrelative to the casing I. The hub .lb

is adapted to receive the end of a propeller shaft P, shown fragmentarily in the figure. Extending forwardly from the casing! so as to cover the webs la and hub lb is a nose 2, which is stream-lined. The rear code! the casing I" is closed by an end plate 3, which is provided A with a sleeve portion 3a. adapted to fit around the propeller shaft P.

Extending inwardly near the forward end of the casing I are propeller blade bearings lc. Two or more of these bearings are provided, depending upon the number of propeller blades it is desired to use. Two propeller blades are shown in the structure illustrated. Rotatably mounted in each bearing I0 is the shaft portion da'of a propeller blade 4. The longitudinal axis of each propeller blade is closer to the leading edge than to the trailing edge thereof so that the center of thrust of the propeller blade is between the axis and the trailing edge. The reason for this will be brought out hereinafter.

The shaft 4a of each propeller extends through its bearing lo, and has secured to its protruding inner end a bevel gear 5. In order to lock the propeller against radial movement, but permitting rotation thereof, a key or locking means 6 in the form of a yoke may be inserted into a slot provided in the bearing Ic so as to fit in a channel 42) provided in the shaft 4a, as shown best in Figs. 2 and 6. This locking means 5 prevents the propeller from leaving the hub casing by reason of centrifugal force.

Rotatably mounted upon the propeller shaft P, between the sleeve 3a and the hub' lb, is a 30' transmitting gear'l, comprising a bevel gear portion 1a and a spur gear portion lb. The bevel gear portion la is adapted to engage all of the propeller blade bevel gears 5, so" that rotation of the transmitting gear causes equal rotation of all the propeller blade gears, whereby the change in pitch of the several propeller blades is equal.

Certain of the webs la support bearings Id arranged in parallel disposed relation to the propeller shaft P. These bearings journal governor shafts 8.

Opposite the spur gear portion lb of the transmitting gear I, each of the shafts 8 is provided with a governor pinion gear 9.

Also supported on each shaft 8 and connected with the corresponding governor gear 9, is a governor arm l0; it is preferred to provide two sets of these governor arms and gears so as to balance the weight about the axis of the propeller shaft. The extended ends of the governor 'arms l0 are provided with cup portions Illa,

Formed in the hub casing I in alinement with the normal axis of each spring II, is a socket or recessed portion I e, having a screwthreaded hole ir'i' its inner end adapted to receive an externally threaded sleeve portion |2a of said anchor l2.

' The sleeve portion I20 is adjustable longitudithe offset relation of the center of pressure to the axis of rotation of the propeller. I

In the structure shown in Fig. 8, the propeller blade l3, while having its axis l3a adjacent its leading edge, is without the fln along its trailing edge, and consequently the torque exerted. on its shaft 13b when the propeller is revolving around the propeller shaft P is less than the torque exerted on the shaft 441 of the propeller, blade 4, under like conditions.

It is well known that the conventional nonvariable pitch propeller requires not only a certain definite speed at which to develop its most emcient thrust, but has but one altitude at which it can develop its maximum thrust. Above and the propeller decreases. With my automatic vari-' able pitch propeller, its efllciency is at a maximum at all altitudes of the airplane and speeds of the engine.

Operation of my automatic variable pitch propeller is as follows:

When the propeller is not revolving, the governor levers I 0 are in the position shown by solid-lines, and the propeller blades are in a position to have but a small pitch. At idling speed, the springs H allow but slight movement of the governor levers in response to the can; trifugal force so that the pitch of the propelms is not materially increased. Due to the fact .blades tend to assume a position of zero pitch,

and' consequently tend to shift the governor levers against the action of centrifugal force.

The engine in rotating overcomes this action until an equilibrium is established, at which the propeller is absorbing all the power available from the engine.

Upon. taking oil,- the'pitch increases slightly as the speed of the airplane picks up, due to the forward motion of the airplane, thus giving nrarimum thrust for the entire period of taking 0 i As the airplane increases its altitude, the density of the air decreases, whereby the pressure of the air which tends to cause the propeller blades to assume a position of zero pitch is reduced. This. causes the governor levers or arms It to shift outwardly so as to compensate for the lowered air density, whereby the propeller blades assume a new and increased pitch.

Thus, the pitch of the propeller changes in in-- verse proportion to the change in air density, increasing in pitch as the airplane ascends and decreasing as the airplane descends. This change in pitch is just sufficient to permit"the propeller to absorb at any altitude all the available power of the engine for any given speed thereof, and deliver the maximum thrust or traction.

Above the critical altitude of the engine where the power thereof decreases, the pitch of the propeller blades decreases also so that the propeller blade can still efficiently apply the lowered power of the engine. .Thus, for all altitudes, even above the critical altitude 'of the engine, the propeller blades automatically assome a pitch capable of most effectively applying the power developed by the engine.

Variation in the pitch of the propeller may .also be 'controlled'by varying thespeed of the engine; at the different speeds, the pitch of the adjacent its shaft portion 4a. This fin increases propeller changes so as' to come .to' an equilibthat the center of thrust of the propeller blades rium at a pitch at which the power of the engine at such speed-is absorbed into the most efllcient thrust. Thus, should it be necessary to decrease the speed of the engine, the propeller delivers the maximum thrust possible from such speed.

Though I have shown and described a particular construction, combination and arrangement of parts and portions, I do not wish to be limited to this particular construction, combination and arrangement, but desire to include in the scope of my in'vention the construction, combination and arrangement substantially as set forth in the appended claim.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

In a variable pitch propeller, a hub secured to the propeller shaft of an engine, a casing secured to said hub and revoluble therewith, propeller blades extending from said casing and rotatable about their longitudinal axes, the centers of thrust of said propeller blades being between their longitudinal axes and their trailing edges, said propeller blades havingtheir major thrust portions near. said casing and decreasing outwardly, a combined bevel and spur gear revbIubIy-mounted on the propeller shaft of the engine in said casing beveled pinions secured to 10 said propeller blades engageable with the beveled portion of said gear, spur pinions revolubly mounted in said casing engageable with the spur portion of said gear and weight and lever means connected with said spur pinionsso constructed 1 and arranged that said propeller blades are shifted with a varying speed of the engine shaft.

. ZELIE RIDDLE. 

